JVC AV-27432 strange noise pattern - Videokarma.org TV - Video

grossbard · #1 10-06-2019, 12:24 PM

I'm back again with a new problem! this time it's on this JVC AV-27432 a family member gave me. It's a great looking set with component, but it has this weird noise pattern that shows up all the time, and it's even more pronounced on the component input.

I took a picture of the noise on a black screen with the brightness turned all the way up so it better appears on the camera. I tried to take a video but my phone doesn't work well when filming CRTs.

The noise pulsates from left to right and the pattern randomly changes in size. I've already replaced all the caps in the power supply, neckboard, and deflection area so I'm not sure what else to try.

Also: the forum rotated the picture 90 degrees counter-clockwise for some reason.

zeno · #2 10-06-2019, 07:01 PM

Thats moire. Try turning down G-2 a little or de focus a tad. Also
brite & contrast.
Almost normal to see it on some tubes. IIRC these sets had RCA CRT's
& they were not known for moire.

73 Zeno

LFOD !

grossbard · #3 10-06-2019, 07:36 PM

I thought moire was more of a static thing that didn't move, but I could be wrong of course! I went ahead and made a video, but it's not very good. however, if you look towards the middle of the screen you can see the noise pattern moving.

I cranked the brightness way up so it would show up on camera, but it can be seen even with the brightness at default.

https://drive.google.com/file/d/1E-b...Gl5J_IjZE/view

old_tv_nut · #4 10-06-2019, 08:44 PM

Just some speculation:
Does this set have a switched-mode power supply?
Could this be a grounding problem?

freakaftr8 · #5 10-06-2019, 11:51 PM

That almost looks like interference. possibly in the front end. Check wiring inside. Move some things around. Possibly shielding is too close to voltage lines picking up DC..

grossbard · #6 10-07-2019, 02:13 PM

Quote:

Originally Posted by old_tv_nut

Just some speculation:
Does this set have a switched-mode power supply?
Could this be a grounding problem?

It was manufactured in 2003 so I assume it has a switchmode ps.. Just to rule out it being a house power issue, I tried running it on a UPS on battery and the interference was still there.

Quote:

Originally Posted by freakaftr8

That almost looks like interference. possibly in the front end. Check wiring inside. Move some things around. Possibly shielding is too close to voltage lines picking up DC..

I tried moving all the cables away from the anode cable but that didn't make a difference...

I wish the camera did a better job of picking up the issue...it's VERY noticeable in person.

freakaftr8 · #7 10-07-2019, 03:19 PM

Was this here before you recapped the whole unit?

grossbard · #8 10-07-2019, 04:04 PM

Quote:

Originally Posted by freakaftr8

Was this here before you recapped the whole unit?

It was. that's why I was hoping a recap might help. Any other parts I should be looking at? I don't own a scope so this may be harder than it needs to be...

old_tv_nut · #9 10-07-2019, 04:09 PM

you might try connecting a clip lead to ground and then touching other ground points on different circuits.

Caution! Before you start working on it while it's live, do you know for sure it's a cold chassis? If not, you will need an isolation transformer.

grossbard · #10 10-07-2019, 04:17 PM

Quote:

Originally Posted by old_tv_nut

you might try connecting a clip lead to ground and then touching other ground points on different circuits.

Caution! Before you start working on it while it's live, do you know for sure it's a cold chassis? If not, you will need an isolation transformer.

Yeah there's definitely a hot/cold side, the chassis is marked pretty well.

Popester · #11 10-07-2019, 09:40 PM

First rule of smart safety was to always, always, always use an isolation transformer when doing any tv or radio service. AA5 radios were transformerless and seems like most of the late seventies to late eighties sets would frequently have a hot chassis.

grossbard · #12 10-08-2019, 08:19 PM

I don't suppose this problem could be due to any bad caps in the tuner or audio sections? because I didn't change those.

old_tv_nut · #13 10-08-2019, 09:03 PM

Quote:

Originally Posted by grossbard

I don't suppose this problem could be due to any bad caps in the tuner or audio sections? because I didn't change those.

Showing up on the component input would indicate the tuner is not involved.

Also CAUTION! some switch-mode sets have a hot chassis or parts of the circuit that are hot, even though they may have a polarized power plug. Best to use an isolation transformer rather than risk your life.

Ed in Tx · #14 10-09-2019, 08:33 AM

I'd be going over every other electrolytic cap not already replaced, with my handy ESR meter. Or without that, dripping a tiny bit of freeze mist or liquid gas from a can of dusting 'air' upside down on each capacitor until I see a big change in that interference and find the culprit. Could be in system control or video circuitry. Just my 3¢.

Electronic M · #15 10-09-2019, 09:36 AM

Those $15 Chinese ESR/component testers on eBay are cheap and handy enough that I wouldn't bother to service a SS device without one...I've quickly found bad caps enough times thanks to mine that as far as I'm concerned it has more than paid for itself.